A sound emitted from a speaker possessed by a device to and from which sounds may be input and output is often input as an echo from a microphone possessed by the device. Possibly such an echo lowers the quality of an input sound signal and makes it difficult to hear a sound as a collection target. Therefore, techniques to suppress echoes have been proposed.
For example, an echo cancelling device disclosed in International Publication Pamphlet No. WO 2007/083349 includes an adaptive filter that subtracts a pseudo echo signal generated from a reception signal from a transmission signal to carry out echo cancelling and a variable attenuator that adds a loss to a residual signal resulting from the echo cancelling by the adaptive filter. Moreover, this echo cancelling device includes an attenuator controller that controls the amount of loss of the variable attenuator on the basis of the result of a determination as to whether or not the state is a double-talk state.
Furthermore, an echo processing device disclosed in Japanese National Publication of International Patent Application No. 2005-531956 applies an in-reception gain to a direct signal to generate an input signal transmitted in an echo generation system, and applies an in-transmission gain to an output signal emitted from the echo generation system to generate a return signal. Furthermore, this echo processing device calculates the in-reception gain and the in-transmission gain on the basis of a coupling variable that forms a characteristic of acoustic coupling existing between the direct signal or the input signal and the output signal.